In the process of manufacturing a metal sheet, such as a steel sheet, the metal sheet is subjected to rolling and cooling steps, in which the metal sheet undergoes deformation, such as warping and/or waving. Accordingly, in order to remedy the deformation, such as warping and/or waving, and thereby to flatten the metal sheet, a roller leveler, which includes a plurality of leveling rolls disposed on upper and lower sides in a staggered state, is used (for example, Patent Document 1).
The roller leveler is configured to pass a metal sheet to be flattened between the lower rolls and the upper rolls, while pushing the upper rolls toward the lower rolls or pushing the lower rolls toward the upper rolls, to repeatedly apply bending to the metal sheet, and thereby to planarize the warping and/or waving of the metal sheet. At this time, the pressing amount of the respective rolls of the roller leveler is suitably set to bend the metal sheet at a yield ratio preferably of 0.7 or more.